1. Field of the Invention
The present invention relates to a liquid crystal display device (LCD), and more particularly, to a mask including an optical absorption layer and a diffraction pattern and a method of manufacturing an LCD using the same that simplifies the manufacturing process thereof.
2. Discussion of the Related Art
Liquid crystal display devices (LCD) that are a type of transmissive flat panel display devices (FPD) are mainly applied to portable electronic apparatuses such as notebook computers, personal digital assistants (PDA) and mobile telephones, and are diffusively applied to high definition televisions (HDTV), digital televisions and thin wall-mounted televisions. In general, various kinds of FPDs such as plasma display panels (PDP), vacuum fluorescent displays (VFD) and field emission displays (FED), together with the above-described LCDs, are actively under study. However, due to such advantages as productivity, driving facility and high picture quality, the LCDs are mainly used.
The LCD is a device that displays information on a screen using refractive index anisotropy of liquid crystal. In general, liquid crystal is provided between a lower substrate on which a driving device is formed and an upper substrate on which a color filter is formed to form a liquid crystal layer. The molecules of the liquid crystal layer are driven by the driving device to control the amount of light that transmits the liquid crystal layer, thereby displaying information on the screen. Among various kinds of LCDs, a thin film transistor (TFT) LCD in which TFTs are used as the driving device is mainly used.
The TFT is formed in each of the pixels of an LCD to independently control the pixels. Such an LCD is manufactured by complicated processes including a photolithography process which requires a photo mask. Therefore, simplification of the manufacturing process is a main concern in reducing the manufacturing cost and improving the yield. As a result, significant efforts have been made in order to simplify the manufacturing process. At the beginning, eight masks had been used to manufacture a TFT-LCD. However, a seven or six mask process was introduced to simplify the manufacturing process, and, recently, a five mask process has been mainly employed to manufacture a TFT-LCD.
FIGS. 1A to 1E illustrate a five mask process to manufacture an LCD according to a related art. A method of manufacturing an LCD will be described in detail with reference to FIGS. 1A to 1E.
First, as illustrated in FIG. 1A, a gate electrode 11 made of metal is formed on a transparent first substrate 10 such as glass. More specifically, after forming a metal layer on the entire substrate 10, the metal layer is coated with photoresist. Then, the photoresist is developed using a first mask, and an etching process is performed to form the gate electrode 11. A gate insulating film 16 is, then, formed on the first substrate 10 on which the gate electrode 11 is formed.
Next, as illustrated in FIG. 1B, a semiconductor material such as amorphous silicon (a-Si) is formed on the gate insulating layer 16 and is etched using a second mask to form a semiconductor layer 13.
Next, as illustrated in FIG. 1C, source/drain electrodes 15 are formed on the semiconductor layer 13. More specifically, after forming a metal layer on the entire semiconductor layer 13 and gate insulating layer 16, the metal layer is coated with photoresist. Then, the photoresist is developed using a third mask, and an etching process is performed to form the source/drain electrodes 15. Although not shown in the drawing, an ohmic contact layer that is an impurity layer is formed between the semiconductor layer 13 and the source/drain electrodes 15.
Next, as illustrated in FIG. 1D, after forming a passivation layer 17 on the entire first substrate 10, a contact hole 18 is formed in the passivation layer 17 using a fourth mask.
Then, as illustrated in FIG. 1E, a transparent electrode such as indium tin oxide (ITO) is formed on the passivation layer 17 and is etched using a fifth mask such that a pixel electrode 19 is formed on the passivation layer 17. At this time, the pixel electrode 19 is connected to the drain electrode 15 through the contact hole 18 formed in the passivation layer 17.
On the other hand, a black matrix 22 and a color filter layer 24 are formed on a second substrate 20, the first substrate 10 and the second substrate 20 are attached to each other, and a liquid crystal layer 30 is provided between the first substrate 10 and the second substrate 20 to complete an LCD.
As described above, the related art method requires five masks for manufacturing an LCD: a mask for the gate electrode, a mask for the semiconductor layer, a mask for the source/drain electrodes, a mask for the contact hole and a mask for the pixel electrode.
Referring to FIG. 2, the above-described five-mask LCD manufacturing process generally uses a mask 40 having a transmissive region and an interceptive region. The interceptive region that blocks light includes metal patterns 42 formed on a substrate 41. The metal patterns are generally formed of metal such as Cr, and quartz is generally used for the substrate 41 for high transmittance. By irradiating light onto a photoresist layer through such a mask and then developing the phtoresist layer, a desired pattern is formed.
Although not shown in the drawings, a photolithography process using a mask is so complicated that the manufacturing cost of an LCD increases and the yield decreases. Therefore, active efforts in reducing the number of a photolithography process have been made.